1. Field of the Invention
The present disclosure generally relates to data communications and data communications systems, and more particularly, to a system and method for efficient transmission of multimedia and data.
2. Description of the Related Art
In many communication systems, data is transmitted in packets (also known as frames). Referring to FIG. 1, a packet 10 often consists of a preamble 12, a header 14 and the payload 16. The preamble 12 is often used for synchronization, channel estimation or for clear channel assessment. The header 14 usually contains data such as source and destination, the length of the payload 18, modulation and coding type 20, etc. Since the correct detection of the information is often essential to receive and deliver the payload, the header 14 is usually heavily protected with different types of redundancy such as a Forward Error Correcting (FEC) code.
When the correct delivery of payload needs to be guaranteed, often a retransmission scheme is used. In other words, a error detecting code (such as a Cyclic Redundancy Check or CRC) is used. Parity bits are calculated at the transmitter and are included in the packet in a data field often called Frame Check Sum or FCS, as illustrated in FIG. 2. At the receiver these parity bits are used to determine whether an error has occurred in the payload. In case of errors, the receiver will ask the transmitter to retransmit all or part of the packet. When correct delivery of data does not need to be guaranteed (“best effort”) the use of such method is not needed.
Normally, the preamble is used for synchronization, channel estimation, and frequency offset estimation. However, when the packet is long, the information estimated during the preamble may no longer be up-to-date when nearing the end of the packet. In this case, a midamble 24 can be placed in the middle of the packet to assist the updating of the channel and frequency offset estimation as well as re-synchronization, as shown In FIG. 3.
In many communication systems, different types of data are needed to be communicated. These different types of data often have different requirements on the error rate, and tolerable delay. As a result, different modulation and coding should be used for different types of data. For example, in the transmission of multimedia, often video, audio, security (encryption) information and control information need to be transmitted. Aside from these different sources, even different data bits from one source (e.g. video) could have different requirements of the error rate.
Hence, it is desirable that different modulation and coding schemes are employed such that different protection levels are provided for the data with different levels of sensitivity. In a conventional packet structure, only one type of modulation and coding can be used. Hence, the different types of data must be transmitted using different packets. This will increase the packet overhead (preamble, header and inter packet guard times), and reduces the efficiency of the system. Therefore, a need exists for techniques for generating a data packet of different types of source data in the same packet enabling efficient transmission of multimedia and data content.